Dry tongue in first half

Asked for Female, 47 Years

After I get up in the morning, I feel my tongue snd throat are too dry. I don't feel hydrated even after drinking 2 to 3 glasses of water. I drink around 2 to 3 litre water.
This had been happening since almost 6 months. Since I am underweight and have constipation, I am taking a protein rich and fibre rich diet but in moderation. Can this be the cause?
I also have thyroid. I am originally hypothyroid from 30 years but 3 months back showed hyperthyroid. I am now on a reduced dose. Can it be that the current dose is still overdose and it may be linked to my thirst in someway.
I also get some blood filled phlegm. In mornings, I have to spit out phlegm sometimes.
Please advise the cause of this symptoms and whom should I consult.

Hello there..... Get plenty of sleep and rest your voice......
Drink fluids. Drink plenty of water to keep the throat moist and prevent dehydration.....
Try comforting foods and beverage. Warm liquids — broth, caffeine-free tea or warm water with honey can soothe a sore throat.
Gargle saltwater. A saltwater gargle of 1 teaspoon. Gargle the solution and then spit it out......